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Comment by Rebelgecko | Hacker News Reader

I don't think you can get a Tesla for $22,000 (USD).

But these low volume (both in terms of # of units sold and SW&P) things get really expensive as high R&D costs are mostly amortized by people who are willing to ride the cutting edge. If you don't have high bandwidth requirements you can get away with some $20 transmitters using LORA or some cheapo ~900mhz transmitters that use amateur frequencies

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> If you don't have high bandwidth requirements

That's a pretty big IF, no?

VHF systems at 455MHz are about 5K Euros and maxes at 9600 Baud.

There was an article on HN recently about a cubesat mission that failed. And the communication system was one of the critical failure points.

We got similar speeds with $5 chips from TI (although the antennas on both ends cost more than $5!). With nicer hardware, speeds in the hundreds of kilobits and megabits are very doable. I'll link a table below from 2015. Back then, megabit speeds were rare but I believe they're marginally more common now. Of course most people aren't hitting their nominal bandwidth amounts.

https://www.klofas.com/comm-table/table.pdf

And how will that TI chip work when hit with space radiation?

And how far down the dbm sensitivity scale are those TI chips?

You completely missed me pointing out that a cubesat-type project failed miserably for reasons relating to all this (Ah, found the link): https://hackaday.com/2020/01/24/lessons-learned-from-a-cubes...

They call it "rocket science" for a reason.

Not great, but it worked serviceably. Most of the chips going into LEO aren't rad hard. There's various techniques for dealing with problems like single event upsets and latchup. For the cubesat formfactor I think watchdogs timers are the most common and require the least overhead.

I think this[1] is the datasheet for the chip that we used (on a custom PCB), I'm not an RF person but maybe that will answer your questions about dbs.

Communication systems are certainly critical, and it's smart to have redundancy like that team did. However it's kinda like backing up your harddrive— redundancy is pointless if you never test it and it ends up not working. Lots of satellites have radio problems. Lots of satellites also don't have radio problems— there's always going to be a small number of random failures, but most of the problems are not insurmountable, especially if you're able to test extensively and iterate

[1]: http://www.ti.com/lit/ds/symlink/cc1101.pdf

LoRa in/from space is a thing [1].

[1] https://lacuna.space/technology

Your low-cost LORA/whatever plan would be foiled by lack of regulatory approval for using those frequencies and those waveforms.

If they're already ISM do they need special approval to use in space?

Yes. https://www.space.com/40001-four-cubesats-unauthorized-launc...

The last time so checked, I could not find anything preventing the use of Lora in space (if you are operating in the UK). However, the frequencies you can use are different over different territories so it is up to your satellite to use the correct ones depending on where it is and what it is pointing at.

I'm not a radio guy so I may be missing some nuances, but in my experience that's not a problem. If you're broadcasting over the whole world, you may have trouble using 915mhz. But if your ground stations are in places where 915mhz is lightly regulated it is no big deal. I think that is the case for the entire western hemisphere. The FCC lets you do pretty much whatever you want in the neighborhood of 915mhz as long as you're not pumping out more than a couple watts.

We've mentioned frequencies and transmitter power in ODAR paperwork but it hasn't been an issue (ODAR is a form that the FCC gets which is mostly there to make sure you don't litter while you're in space).

Edit: Actually I looked into this and we had to a bit more paperwork than just the ODAR. The FCC also wanted to know about signal modulation and ground station locations.

Even if you succeed in using ISM frequencies "without paperwork" (not gonna happen) would you be really happy about investing in a satellite which is parked in the middle of massive terrestrial interference?

When we went through the FCC ELS it certainly wasn't "without paperwork". But most of the paperwork was just reformatting engineering work that needed to be done regardless of the FCC process.

"where is the transmitter going to be?"

"where is the receiver going to be?"

"how is the cubesat going to be disposed of?"

"what frequencies will be used?"

"does anyone on the team do DRUGS?"

etc

The whole process took a couple months, with IMO is fairly lightweight for a massive government bureaucracy like the FCC

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